A DNA based vaccine containing HIV-1 Env and Rev genes was tested for safety and host immune response in 15HIV-infected asymptomatic patients the CD4-positive lymphocyte counts >=500ul of blood and receiving no antiviral therapy. Successive groups of patients received three doses of vaccine at 30, 100, or 300-ug at 10-week intervals in a dose-escalation trial. Some changes were noted in cytotoxic T-lymphocyte activity against gp 160-bearing targets. Importantly, enhanced specific lymphocyte proliferative activity against HIV-1 envelope was observed in multiple patients. Three of three patients in the 300-ug dose group also developed increased MIP-a levels which were detectable in their serum. Interestingly, patients in the lowest dose group showed no overall changes in the immune parameters measured. The majority of patients who exhibited increased in any immune parameters were contained within the 300-ug, which was the highest dose group. These studies support further investigation of this technolgoy for the production of antigen-specific immune responses in humans.